December 7, 2022

Genetic predisposition as a legal defence

What is the relationship between genetic predisposition and upbringing?

With the rapid advance of behavioural genetics it has become easier for lawyers to mount a defence based on ‘genetic predispositions’. A number of high profile cases in the US have involved such defences, including the recent trial and conviction of gunman Jared Lee Loughner. If a genetic predisposition can be demonstrated, a defence can secure a significantly more lenient sentence, and as is too often the case, prevent their client from receiving the death penalty. 

The genetic defence has received significant attention from academics, as it throws up a number of complex philosophical questions: What is the relationship between genetic predisposition and upbringing? What effect does this have on gene expression? Can you quantify the effect of genetics on culpability? And do we have an adequate legal framework to do so?

The media has ridiculed the genetics defence, but experts say it is valid. “People don’t have the degree of control over their behaviour that we thought,” says Fordham University law professor Deborah Denno. “That doesn’t mean to suggest that there’s no control over their behavior – but that some of us have higher hurdles than others.” Four US academics have just released a co-authored book discussing the interaction between environmental factors and genetics in determining violent crime.

Unfortunately many judges are yet to be educated on the nature and reliability of evidence from behavioral genetics. There are some courses available, but by and large, the calls of academics for education of the judiciary have gone unheeded.  

Xavier Symons
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genetics and law